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Compressor Non-return Valve

I have an old Ingersoll-Rand single phase compressor without a reservoir.
Model WB100, 240V, 4.3 A (Perhaps 1/2 HP).
I am using it with a short air line to pressurize a model locomotive boiler to 20 psi for an initial appraisal of boiler condition.
I can only get about 10 psi because of either boiler leaks or compressor problems.
When I turn off the compressor to listen for air leaks from the boiler (more likely various valves and cocks), I can hear the compressor venting the line internally, and the boiler, down very quickly.

Is output line venting when turned off normal for compressors of this type ?
The output appears to be 1/4" NPT, any suggestions on where to get a non-return valve ?

I have available a small (say 5 litre) high-pressure personal oxygen cylinder that is no longer required.
Is it advisable to use this as a reservoir for the compressor ?

I have an old Ingersoll-Rand single phase compressor without a reservoir.
Model WB100, 240V, 4.3 A (Perhaps 1/2 HP).
I am using it with a short air line to pressurize a model locomotive boiler to 20 psi for an initial appraisal of boiler condition.
I can only get about 10 psi because of either boiler leaks or compressor problems.
When I turn off the compressor to listen for air leaks from the boiler (more likely various valves and cocks), I can hear the compressor venting the line internally, and the boiler, down very quickly.

Is output line venting when turned off normal for compressors of this type ?
The output appears to be 1/4" NPT, any suggestions on where to get a non-return valve ?

I have available a small (say 5 litre) high-pressure personal oxygen cylinder that is no longer required.
Is it advisable to use this as a reservoir for the compressor ?

John.

1 - not a good idea to use air to test a boiler. It may explode. Use water instead to test your boiler. That said....

2 - all reciprocating (piston) compressors do vent the pressure line from the compressor. This venting is done by the pressure switch. Where the pressure line enters the storage vessel is a one way valve, which prevents the storage vessel to be vented as well. Without this venting, the electric motor would need a very high starting torque to overcome the pressure in the cylinder. In your case, you simply would have to add a one way valve before the air enters your boiler. It would then act as an air storage vessel.

Does your compressor have a pressure switch? If it doesn't and you are using just the 'air pump', then the outlet valve is leaking back into the cylinder and past the piston rings into the crankcase. These valves are usually reed valves and wear or crack.
If you do have a poressure switch on it, then there should be a non-return valve between the compressor head and it and it's leaking, if not, time to take the head off the compressor and have a look at the valve(s).

Cheers, Joeagain completely retired - more time to contemplate projects and spend more shed time....

Thanks guys for the comments.
There is a pressure adjustment knob, presumably on a screw-down regulator, and it makes sense that the output line should vent when switched off.
I will source a non-return valve today.

In the live-steam hobby it is entirely normal to test locomotives on the bench with compressed air, at a limited pressure of course.
The hydraulic test is done initially for a new boiler at 200% operating pressure to prove boiler integrity and to investigate any leaks.
Subsequent re-tests are done periodically at 150% to maintain certification within the hobby.
Typical leaks on older copper boilers are threaded fittings and pin-holes in silver soldered joints.

The subject boiler is on a recently acquired loco that was OK when last steamed 13 years ago.
Before I waste time with the boiler inspector and sealing the boiler for a hydraulic, I want to see it operate in case there are other issues.
If the loco is Ok, it should operate on the bench easily at 20 psi, and may continue to operate at less than this.

It is definitely not a good idea to use air to test a boiler. It may explode. If you have ever seen a boiler burst under steam pressure, its not a pretty sight. Use water instead to test your boiler. You might get wet but its far better that, than the shrapnel that could come your way...

I have an old Ingersoll-Rand single phase compressor without a reservoir.
Model WB100, 240V, 4.3 A (Perhaps 1/2 HP).
I am using it with a short air line to pressurize a model locomotive boiler to 20 psi for an initial appraisal of boiler condition.
I can only get about 10 psi because of either boiler leaks or compressor problems.
When I turn off the compressor to listen for air leaks from the boiler (more likely various valves and cocks), I can hear the compressor venting the line internally, and the boiler, down very quickly.

John.

Sounds like the valves are worn in the head. So unless you fix them it won't pump up very well.

An old Ingersoll Rand I had used poppet valves in the head. Once the guides get worn they wobble all over the place and may not seal.

An LPG gas cyclinder makes a good tank. They are rated at over 200 psi. The oxygen cyclinder should be rated even higher.

A fellow member of the Forum contacted me and offered to give me a Taurus 30 litre compressor that he had acquired from a third party.
The compressor was without the cylinder/motor unit, apparently due to operation without oil, but otherwise complete.
I rigged up the Ingersoll-Rand to feed the reservoir, safety valve and regulator, then on to the loco.
The reservoir seals fine, but the Ingersoll-Rand could not get past 20 psi.

I connected the reservoir to the loco and the boiler and reservoir dropped to about 15 psi.
Opened the throttle, and got a few wheel revolutions before running out of air.
I won't test the loco again until I arrange some cylinder lubrication (air line oil).

Well, I got some airline oil into the loco cylinders and got a few revolutions on several pump-up and test cycles, the loco operates fine.

The I-R compressor is now in bits, it has a bakelite (world's first synthetic plastic) cylinder, a rubber feather-edge or slightly rounded piston seal, and thin metallic flap valves.
The bakelite is quite scratched and the flap valves have some dirt build-up.

Most of the cylinder scratches are confined to about 1/4 of the periphery, probably corresponding to one side of the piston thrust.
Unfortunately, I didn't mark the position of the cylinder before it fell out on dis-assembly.
The piston seal has significant scaring.

The valves look like they will clean up fine.
I can arrange a holder in the lathe for the cylinder to apply a lap/polish procedure.
However, a replacement seal for the piston could be a problem.
The seal has a tapered contact with the cylinder about 4 mm long, thickness is about 1 mm visible and a diameter of about 60 mm.

Any suggestions on where to look for a piston seal, and what cutting compound to use on the bakelite ?

The maker probably sells a service kit with everything needed for a 10000h service. These oil free compressors need new parts at regular intervals. The good ones that is, cheapies are regarded as disposable.

Well, I got some airline oil into the loco cylinders and got a few revolutions on several pump-up and test cycles, the loco operates fine.

The I-R compressor is now in bits, it has a bakelite (world's first synthetic plastic) cylinder, a rubber feather-edge or slightly rounded piston seal, and thin metallic flap valves.
The bakelite is quite scratched and the flap valves have some dirt build-up.

Most of the cylinder scratches are confined to about 1/4 of the periphery, probably corresponding to one side of the piston thrust.
Unfortunately, I didn't mark the position of the cylinder before it fell out on dis-assembly.
The piston seal has significant scaring.

John.

The seal looks OK in the photo.

I'd be trying to machine up a replacement cylinder out of brass or stainless to save spending money.

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